This invention relates to an engine ignition apparatus and, more particularly, to an ignitor for an internal combustion engine.
FIG. 9 is a sectional side view of a known ignitor for an internal combustion engine in which a base 1 is made of a metal such as aluminum and adapted to be securely mounted to an internal combustion engine (not shown). The base 1 has a bearing 1c for rotatably supporting a rotary shaft 3 which is adapted at one end 3a to be operably connected to and rotate in synchronization with an engine crankshaft (not shown). The base 1 has a first substantially planar top surface 1a, and vertically extending support posts 1b having a threaded hole 1d for receiving a screw 32 therein for the purpose which will become apparent later.
Disposed on the top surface 1a of the base 1 is an ignition coil unit 20. The ignition coil unit 20 has a central bore 20a through which the rotary shaft 3 extends. The ignition coil unit 20 also has primary and secondary coils (not shown) and an iron core (not shown).
The ignition coil unit 20 has a connector terminal 20b extending perpendicularly to the top surface 20c of the ignition coil unit 20 for electrical connection to the central electrode 10 disposed within a cap 2 which covers an opening of the base 1 and the ignition coil 20 together with other components. The cap 2 has a plurality of circumferential electrodes 12 to be connected to spark plugs (not shown) of an internal combustion engine (not shown).
A control unit 4 is disposed on the ignition coil unit 20. As illustrated in FIGS. 10 and 11, the control unit 4 is a substantially disc-shaped member and has a central bore 4d for allowing the rotary shaft 3 to extend therethrough and through holes 4e formed in the flange 4f for receiving the mounting screw 32 (See FIG. 9). FIG. 11 is a side view of the control unit 4 illustrated in FIG. 10. The control unit 4 comprises a base plate 4a having an aluminum heat sink 22 as illustrated in FIG. 13 attached at its bottom as shown in FIG. 9. The heat sink 22 has through holes 33 for receiving dowels 34 formed on the bottom of the base plate 4a as illustrated in FIG. 11. The control unit 4 also comprises a crank angle sensor 40 disposed on the base plate 4a for detecting a turning angle of the engine crank shaft (not shown) and a power switch for controlling a primary current to the ignition coil The crank angle sensor 40 comprises first and second Hall-effect IC sensors as magnetic sensors (not shown) and first and second magnets (not shown).
As illustrated in FIG. 12, the power switch 21 comprises a hybrid integrated circuit (HIC) 23 disposed on the heat sink 22 of the base plate 4a for controlling a primary current flowing through a primary coil of the ignition coil unit 20, and a power transistor 24 disposed on the heat sink 22 for interrupting or passing through a primary current for flowing through a primary coil of the ignition coil unit 20.
FIG. 14 is a sectional view of the control unit 4 taken along line XIV-XIV in FIG. 10. As illustrated in FIG. 14, an insulating plate 26 is disposed on the heat sink 22 of the base plate 4a for insulating the power transistor 24 from the heat sink 22. Disposed between the power transistor 24 and the insulating plate 26 is a heat sink 55. The heat sink 55 has a coefficient of thermal expansion between those of the power transistor 24 and the insulating plate 26. The power transistor 24 and the HIC 23 (See FIG. 12) is covered with a resin 52 such as silicone which is comparatively soft for preventing a stress from outside and facilitating a radiation of heat. An insert conductor 51 is disposed within the base plate 4a and has one end within the power switch cavity electrically connected to a lead 50 extending from the power transistor 24. The other end of the insert conductor 51 is electrically connected to a connector for external connection.
As illustrated in FIG. 9, the first and the second disc plates 5 and 15, which are two concentric disc-shaped member made of magnetic material, are fixed to the top end of the rotary shaft 3 by means of a screw 7 and a blank 6 formed on the top end of the rotary shaft 3 so that the first and second disc plates 5 and 15 synchronously rotate therewith. Both of the first and second disc plates 5 and 15 have folding portions 5a and 15a at their edges respectively which are folded perpendicularly thereto. The folding portions 5a and 15a pass respectively through first and second grooves 8 and 18, illustrated in FIGS. 9 and 10, both formed between the Hall-effect IC sensors (not shown) and magnets (not shown) of the crank angle sensor 40.
Securely mounted on the blank 6 is a distributor rotor 9 which rotates synchronously with the rotary shaft 3 for distributing the high-tension secondary voltage supplied from the ignition coil unit 20. The rotor 9 has rotor electrode 11 disposed on the top thereof. The rotor 9 and other components are covered by a cap 2, as described above, which is attached to the control unit 4 by means of mounting brackets 2b having a through hole 2c for receiving the mounting screw 32 therein. As illustrated in FIG. 9, the center electrode 10 disposed within the cap 2 is electrically connected to the rotor electrode 11 of the rotor 9. A plurality of circumferential electrodes 12 are disposed within the cap 2 for each spark plug of cylinder of the internal combustion engine (not shown) for distributing a secondary voltage from the ignition coil unit 20 through the rotor electrode 11 in turn to ignite the spark plugs.
In the known ignitor as described above, when the rotary shaft 3 rotates synchronously with the engine crank shaft (not shown) of the internal combustion engine, the first and second disc plates 5 and 15 disposed thereon ere also rotated synchronously. As the folding portion 5a and 15a pass through the first and second grooves 8 and 18, a magnetic flux from the first and second magnets (not shown) to the first and the second Hall-effect IC sensors (not shown) is interrupted by the folding portion 5a and 15a. The first and the second Hall-effect IC sensors detect this as a change of the magnetic flux in relation to the rotation of the rotary shaft 3. The first Hall-effect IC sensor converts the change of the magnetic flux to electronic signals to be supplied to a control computer (not shown). The electronic signals are processed by the control computer and transmitted to the power switch 21 which comprises the HIC 23 and the power transistor 24. As the result, the primary current of the ignition coil unit 20 is controlled, and, a secondary voltage are created in the ignition coil unit 20 on an ignition timing. The secondary voltage is distributed to the circumferential electrodes 12 in turn through the center electrode 10 and the rotor electrode 11 accompanying with the rotation of the rotor 9. The spark plugs of the cylinder is ignited in turn and the internal combustion engine operates continuously.
On the other hand, the second Hall-effect IC sensor converts the above change of the magnetic flux to electronic signals so that the electronic signals are supplied for identifying the engine cylinder.
During assembly of the known ignitor as above described, when the power switch 21 is assembled on the heat sink 22, firstly the HIC 23 and the power transistor 24 are fixed on the heat sink 22 as illustrated in FIG. 13 and the leads 50 and 53, each connected to the HIC 23 and the power transistor 24 respectively by for example solder, are electrically connected to the leads such as 51 which extend to the crank angle sensor unit 40 or the like. Further, the heat sink 55 which has a coefficient of thermal expansion between those of the power transistor 24 and the insulating plate 26, must be disposed between the power transistor 24 and the insulating plate 26 for absorbing the difference in the coefficients of thermal expansion of the power transistor 24 and the insulating plate 26. The heat sink 55 and the insulating plate 26 ere made of a material having a high thermal conductivity. Next, the HIC 23 and the power transistor 24 are covered with the soft resin 52 such as silicone for a protection from outside stresses. However, the resin 52 is not enough for protecting. So, the power switch 21 must be provided with a hermetic cover 21a.
During assembly of the above known ignitor, before the power transistor 24 is fixed with a solder on the aluminum heat sink 22, a surface of the a surface of the heat sink 22 should be plated for soldering. As the heat sink 22 is large as illustrated in FIG. 13, it is hard to heat the heat sink 22 to a temperature high enough for soldering.
As illustrated in FIG. 13, during welding or soldering for an electrical conductor connection, the power transistor 24 and the HIC 23 are exposed. Welding dust therefore which is generated during welding can adhere to surfaces of the power transistor 24 and the HIC 23. Ambient moisture can also enter into these components. If the dust or moisture is attached to these components, they will happen to be damaged. So, several minute assembly processes with substantial attention to dust and moisture contamination are necessary. Many electrical connecting processes between the components on the heat sink 22 are needed during assembly. Even the soft resin 52, may prove inadequate for protecting the connections. Therefore the reliability is not good and the assembly processes are not efficient.